The muggy weather has created ideal conditions for mosquitoes to feast on Londoners as they sleep or enjoy spending evenings outside.
Experts said the warm weather and high water table has caused a “perfect storm” for biting insects, which also includes horseflies and midges.
The insects usually disappear when it is warm and dry, but because of the recent thunderstorms they are hanging around a lot longer.
Temperatures are set to rise further this week and on Friday more rain is forecast.
People working in allotments and gardens are advised them to wear long-sleeved clothing for protection.
London heatwave - July 2015
Matthew Oates, a naturalist and entomologist at the National Trust, said: “This is a very bad year for biters - horseflies and mosquitoes.
“The water table is high thanks to the winter’s rain, there’s no real drought prospect, and even the lawns are still very green.
“The conditions have created a perfect storm for biting insects.”
Dr James Logan, of the London School of Hygiene & Tropical Medicine said: “There was a study recently that showed that the increased use of garden water butts was to blame as they provide perfect breeding conditions.”
